Chemical and Physical Properties of Biomass Pyrolysis Liquids

At RTI International, our advanced biofuels pathway integrates catalytic biomass pyrolysis and hydroprocessing to produce infrastructure compatible biofuels and bioproducts. During the primary direct liquefaction step, catalysts are applied, and process conditions are optimized to maximize the yield and adjust the chemical composition of the liquid biocrude intermediate. Biocrude quality is typically described by the amount of oxygen contained in the organic liquid. The driver for removing oxygen during biomass pyrolysis is to produce biocrude that can be upgraded using conventional hydroprocessing technology, but biocrude is a complex mixture of hundreds of compounds with a wide boiling range and molecular weight distribution. Maintaining oxygen in the biocrude increases yield while these oxygenates can be a source of high value bioproducts if they can be recovered efficiently and cost-effectively. New strategies are being evaluated for upgrading biocrude and recovering bioproducts that look beyond bulk oxygen content.

Oxygen content is also directly proportional to upgrading hydrogen demand but the type of oxygenated compounds are proving important to understanding catalyst fouling during upgrading. Separating biocrude into different fractions with narrower boiling ranges and molecular weight distributions could segregate undesirable components and provide flexibility to utilize different catalysts and process conditions for upgrading each fraction separately to maximize carbon efficiency, minimize hydrogen consumption, and potentially recover higher value bioproducts.

This presentation will focus on the impact of feedstock variety and process conditions on biocrude yield in RTI’s 1 ton/day catalytic biomass pyrolysis unit and biocrude fractionation to support upgrading strategy development in RTI’s pilot-scale hydroprocessing unit. While clear relationships between biocrude composition and upgrading performance are emerging, the goal is to maintain hydrodeoxygenation activity for longer times on stream and avoid reactor plugging. Collectively, these technical advancements are increasing the commercial viability of this integrated advanced biofuels technology pathway.